The invention relates to a laser beam machine wherein a length of an optical path of laser beam is almost constant in spite of a moved position of a machining head.
In a laser beam machine, a workpiece is machined while a machining head being moved. If a length of an optical path of laser beam changes together with a movement of a machining head, degree of collecting laser beam changes, so that it is difficult to maintain a quality of machining to be constant. Due to this reason, various kinds of laser beam machines having almost constant length of the optical path of laser beam in spite of a moved position of a machining head have been proposed (see Japanese patent applications, Publication numbers 2002-336979 and 1996(H8)-52587).
FIG. 8 is a typical view showing a structure of a conventional laser beam machine. A reference number 200 of FIG. 8 is a laser beam oscillator for generating laser beam, and a reference number 201 is a machining head for radiating laser beam on a workpiece, while being moved and driven. A reference number 202 is a machining table for locating a workpiece thereon, and reference numbers 203, 204 are beam guide portions for guiding laser beam from the laser beam oscillator 200 to the machining head 201. At a position near the laser beam oscillator 200, a reflecting mirror 205a is located, at an end portion of the beam guide portion 203, reflecting mirrors 205b, 205e are located, in an inside of the beam guide portion 203, reflecting mirrors 205c, 205d are located so as to face both reflecting mirrors 205b, 205e, at a position facing the reflecting mirror 205e, a reflecting mirror 205f is located, and at a position facing the reflecting mirror 205f, a reflecting mirror 205g is located on the side of the beam guide portion 204. With this structure, laser beam L generated by the laser beam oscillator 200 is reflected by the reflecting mirrors 205a, 205b, 205c, 205d, 205e, 205f, and 205g in this order so as to reach the machining head 201. The reflecting mirrors 205c, 205d are supported by a block 206 for adjusting a length of an optical path, and are moved according to quantity of movement of the machining head 201, so that the length of the optical path from the laser beam oscillator 200 to the machining head 201 is maintained to be almost constant.
Although quality of machining can be maintained to be constant if the length of the optical path from the laser beam oscillator 200 to the machining head 201 can be made almost constant, the shorter the length of the optical path is, the better the quality of machining is. That is, the shorter and almost constant length of the optical path is, good.
In such a laser beam machine, at least two reflecting mirrors 205e, 205f are located between “the reflecting mirror 205d for adjusting a length of an optical path” and “the reflecting mirror 205g on the beam guide portion 204 side”, and laser beam reaches the beam guide portion 204 after taking a long path as shown with an arrow A. Then, the length of the optical path of laser beam becomes longer due to taking a long way, so that a quality of machining decreases.
Besides, it is necessary to seal the beam guide portions 203, 204 so as not to enter dusts and the like therein. When using bellows for sealing, the bellows is easy to be damaged due to repetitive driving, and the durability is low.
Then, a laser beam machine for preventing deterioration of quality of machining by making a length of an optical path of laser beam short and almost constant is still desired. Besides, a laser beam machine having superior durability is still desired.